Innovation in Power & Energy

Within the field of power and energy, the IEL has focused the research activity of the last decade on the development of technologies for the seamless integration of renewable energy resources into the future power grid and, more broadly, to improve the energy efficiency of high-power energy conversion systems. By looking at the broad research field of power and energy from components towards systems, the IEL has provided the fundamental innovations listed below.

In the field of high power switching devices, the IEL PowerLab, has demonstrated the first vertical power GaN transistor grown on cost-effective 6-inch silicon substrate by MOCVD, exhibiting excellent performance with enhancement-mode operation and breakdown voltage of 645 V. In addition, we have also demonstrated high voltage GaN-on-Si PiN diodes, with state of the art figure of merit of 2.0 GW/cm2, which is six times larger than the highest value reported for GaN-on-Si vertical diodes. These results offer a major step towards high-performance GaN vertical devices on low-cost silicon substrates. The powerlab has also proposed and demonstrated the new concept of slanted tri-gates to enhance the breakdown voltage in lateral GaN power devices, which led to an increase of ˜500 V in breakdown voltage compared with the counterpart planar devices. These devices presented a high breakdown voltage of 1350 V with a much smaller size, along with a record high-power figure-of-merit of 1.2 GW/cm2 among GaN-on-silicon lateral transistors. This technology was applied for GaN-on-Si power Schottky barrier diodes resulting in ultra-low leakage current of 51 nA/mm at -1000 V, and a remarkably high breakdown voltage of 2000V, constituting a significant breakthrough from existing technologies.

The IEL Power Electronics laboratory has focused on high-power drives and conversion systems. Within the research in domain of medium voltage high power conversion technologies, this laboratory has proposed several novel converter topologies. Integration of the line frequency transformer into the structure of the modular multilevel converter (MMC) resulted in a new architecture for Galvanically Isolated Modular Converter (GIMC) for MVDC-LVAC conversion. A recently developed MVDC-LVDC high power converter, which utilizes medium frequency operated Scott-Transformer Connection, has allowed to file a joint patent with Hyundai Electric. In the domain of magnetic components modelling and optimization, several improvements of the classical hysteresis Preisach Model have been developed considering both frequency independent and dependent losses, providing improved models for transient electric circuit simulations. Finally, work on optimal design of high power medium frequency transformers for solid state transformers, has been gaining significant visibility and has resulted in four tutorials given in the last years during major power electronics conferences (EPE2017, ECCE2017, Ee2017 and ICIT 2018).

Within the field of smart grids planning operation and control, the Distributed Electrical Systems laboratory (DESL) has developed multiple innovations. The first one consists in new algorithms and devices for the estimation of the so-called synchrophasors. The DESL developed the first phasor measurement unit (PMU) for active distribution networks. The innovation came from algorithms that, for the first time, were able to perform measurements of synchrophasors with parts-per-millions accuracy levels irrespective of the signal dynamics and distortion. These devices opened a new way to operate electrical distribution networks by integrating monitoring, protection and control functionalities, which is an essential step for the massive deployment of distributed renewable energy sources. On the subject of state estimation of active distribution grids, the DESL has been the first in proposing real-time PMU-based state estimation processes for active distribution networks. Concerning the topic of real-time control of active distribution networks, within a join collaboration with the EPFL Computer Communications and Applications Laboratory 2, the DESL has proposed a framework called COMMELC – Composable method for real-time control of active distribution networks with explicit power setpoints. It targets to control an electrical grid in real time, even if the grid has very little inertia, as is typical when there is a large amount of distributed generation. The framework provides an operating system for power grids that allows device controllers for intelligent buildings, e-car charging systems, etc. to be easily connected and provide real time support to the local and bulk power grid. The peculiarity of this framework is that it allows to directly control the targeted grid by defining explicit and real-time setpoints for active/reactive power absorptions/injections obtained by solving an optimization problem. The framework is capable to solve this challenging problem by introducing a common abstract model and a dedicated aggregation process protocol. A formal aggregation method is also proposed in a way such that subsystems can be aggregated into virtual devices that hide their internal complexity. It has been formally shown that the proposed method can easily cope with systems of any size or complexity. This control framework has been the first proposed to treat the problem of real-time control of power grids (i.e., with refresh rates of hundreds of ms) using explicit control setpoints obtained from the solution of an optimization problem. Another fundamental contribution of the DESL concerns the topic of advanced signal processing for fault-location procedures in active distribution networks. The innovation is based on the determination of the time-invariant characteristics of post-fault signals. The DESL, in a joint collaboration led by the Electromagnetic compatibility lab, has proposed a fault-location procedure based on the analysis of the electromagnetic transients originated by the fault and associated with the traveling waves triggered by the fault itself. The procedure was the first to introduce the idea of time reversal in fault-location. The resulting algorithms have been implemented into a new class of smart relays integrating protection and fault-location functionalities.